Injection method for administering microparticles containing active substances to plants

ABSTRACT

A process for the administration of a flowable solid, semisolid, or liquid medium exhibiting a controlled release of at least one active substance to plants by means of injection using needle-free, pressure-actuated devices is characterized in that the medium comprises active substance-containing microparticles of a maximum size of 100 μm including the following components: 
     a) 0.5-70%-wt. of at least one active substance, 
     b) 10-70%-wt. of at least one biodegradable polymer, 
     c) up to 20%-wt. of formulation adjuvants.

The present invention relates to a process for the administration ofactive substance-containing flowable, solid, semisolid, or liquid mediahaving a controlled release of at least one active substance to plantsby means of injection using needle-free pressure-actuated devices.

It is known in the art to use needle-free pressure-actuated injectiondevices for the administration of bioactive substances to plants. Forexample, DE-OS 25 55 092 describes the use of pressure injectors with aplurality of injection nozzles for the treatment of plants. U.S. Pat.No. 3,069,809 also describes pressure-actuated injection devices withoutinjection cannulae by means of which active substances are brought intoplants.

The use of needle-free high-pressure injectors represents a favorablealternative to conventional injection processes. Owing to the fact thatrelatively high-viscous media can be injected by means of theneedle-free injection technique, it is also possible to inject polymericliquids into plants to be treated. This is of particular importancesince the injection medium may be a formulation having controlledrelease properties. Another advantage of this needle-free injectiontechnique and its corresponding devices, which are capable of creatingvery high pressures, is the possibility of treating plants having arelatively thick wood-body.

It is also known to administer controlled-release active substancepreparations to plants by injecting particulate active substancecarriers. U.S. Pat. No. 5 275 819 describes a feed system forbiologically active substances to living organisms (humans, animals,plants). This feed system is to be administered enterically (injectableor implantable). The known device consists of a plurality of naturalactive substance-containing microbeads (microspheres), i.e. thoseoccurring in animal or plant organisms, which release active substancesin a controlled manner when in use.

U.S. Pat. No. 4 690 682 describes an active substance delivery systemachieving a delayed active substance release in human, animal or plantbodies. In this case, injectable active substance-containingmicrocapsuies are concerned which have a size between 0.1 and 3.0 μm anda porous, release-controlling membrane.

Both documents point out the advantages of microencapsulating activesubstances in the administration to living organisms, inter alia toplants; these in particular include increase in stability, fixation ofvolatile substances, and reduction of toxicity. In particular toxicityreduction is of decisive importance for an administration form whenplants are injected with active substances of relatively high phytotoxicpotential; this is documented in relevant literature (F. Muller,"Phytopharmakologie"), for example.

Moreover, microencapsulating the injectable substances ensures that theyare not directly influenced by the plant metabolism. It is known thatthere are several factors impairing or limiting the distribution oforganic compounds in the plant, in particular when it takes place in thephloem. These factors in particular include adsorption, formation ofcomplexes and conjugates, and release from the sieve tubes intoneighboring sieve parenchyma cells which may have a detrimental effecton the transport of exogenous substances.

However, it is pointed out in this context that--in contrast to externalapplications such as spraying processes--the risks connected with theinjection of encapsulated active substances cannot completely beexcluded. The properties of the polymeric starting materials used, e.g.,low decomposition rate, plant intolerance, as well as the particlecharacteristics, e.g., particle diameter, represent factors which mayhave a negative effect on the mobility of the substances which arephloem-mobile per se.

However, to develop a protective or therapeutic effect active substancesmust reach their sites of action in sufficient amounts. As aconsequence, capability of being translocated is of particularimportance.

To distribute the injected microparticles efficiently in conductivepaths of the plant, their size and/or chemical composition as well asthe insertion depth is of importance. This is particularly true forplants having secondary growth in thickness, such as woody plantswherein primary and secondary wood parenchyma rays, in which mainlyorganic compounds are transported, run through the wood at differingdepths. To penetrate a thick wood-body often having several annualrings, and to control the insertion depth, suitable feed systems arerequired. High-pressure injectors known in the art are used as suitablefeed systems for this purpose.

In the application of active substance-containing microparticles toplants most attention has been paid to their use on plant surfacesrather than to their enteric administration, such as injection orimplantation. For this reason, the significance of suitable polymericstarting materials has not sufficiently been examined or described inthe art. In this connection, the state of the art merely mentionsnatural microspheres (pollen, spores) and natural or syntheticpolysaccharides (for example, sodium alginate, calcium alginate,pectins, carragheenan).

There is scarce knowledge of the influence of particle size on theparticles' capability of being translocated. It cannot be excluded thatan increasing particle diameter impairs the mobility of the particulateactive substance carriers in the plant.

At present, there are no satisfactory solutions meeting the demand forparticulate injection systems providing controlled active substancerelease within plant organisms.

It is accordingly the object of the present invention to provide aprocess which can realize the above-mentioned goal of efficientlydistributing the injected microparticles within paths of conduction of aplant. According to the present invention this object is achieved by aprocess according to the features of claim 1.

The present invention and its advantages will be illustrated in thefollowing.

The present invention relates to a process for the administration ofactive substance-containing microparticles having a maximum size of 100μm to release an effective amount of the active substance within apredetermined period by means of injection using needle-free,pressure-actuated devices, the particles comprising one or severalactive substances in admixture with one or several biodegradablepolymers or copolymers as well as suitable additives in the followingcomposition:

a) 0.5-70%-wt. of at least one active substance,

b) 10-70%-wt. of at least one biodegradable polymer,

c) up to 20%-wt. of formulation aids.

According to the present invention the term"microparticles" means bothreal microcapsules, i.e., microparticles wherein an active substancecore is surrounded by a polymer matrix, and monolithic microcapsules(microspheres), wherein an active substance is homogeneously distributedwithin a polymer matrix. According to the present invention the term"biologically degradable", which is equivalent to "biodegradable", means"degradable by stimulation through a biologically active environment".These mean compounds which are both available to the metabolism ofhigher plants and metabolizable by microbes. Any biodegradable polymermay be used to manufacture the microparticles used in the processaccording to the present invention.

Examples include:

aliphatic polyesters, such as poly-E-caprolactone (TONE® P787),poly-3-hydroxybutanoic acid copolymers, poly-3-hydroxyvaleric acidcopolymers, polyethylene succinate, polybutylene succinate (BIONOLLE®)

polysaccharides, such as starch, sodium alginate (MANUCOL® LB) calciumalginate, carragheenan, and pectins

cellulose and its derivatives, e.g., mixed esters, cellulose acetatebutyrate

polylactic acid and polyglycolic acid and their derivatives, such aspoly-L-lactide, poly-D,L,-lactide, and lactide-glycolide copolymers.

The ratio between the polymeric active substance carrier material andthe active substances may vary according to the desired effect; however,it must correspond to the composition as defined in claim 1.

A preferred embodiment of the particles used in the process according tothe present invention has the following components:

a) 35-60%-wt. of an active substance

b) 45-50%-wt. of a biodegradable polymer

c) 5-10%-wt. of additives.

Biological degradation leads to simultaneous active substance release,and it is initiated by hydrolytic and/or enzymatic bioerosion in theplant. Degradation of the products applied by means of the processaccording to the present invention mainly results in fragments that areknown as to their biocompatibility and which can be metabolized innatural metabolic pathways of the plant. Intensity and scope of particledecomposition in the plant organism depend on the kind of polymericmaterials used. Thus, their period of degradation can be adapted to theindicated requirements by adequate choice of starting materials. Thisproperty particularly suits the diversity of individually requiredactive substance supply found in plant cultivation. For example, indiseases involving a high degree of initial infestation, water-solubleparticulate active substance carriers, e.g., made of specificpolysaccharides, may be used which are subject to a relatively rapidhydrolytic degradation under the conditions prevailing in the conductivepaths of the plant. The resulting rapid active substance release resultsin the desired rapid onset of action.

Active substance release from the microparticles used in the processaccording to the present invention cannot only take place by bioerosionof the polymeric carrier, but also by diffusion from the polymericmatrix. This is the case in particular when the particles are formed asmicrospherules, i.e., when the active substance is physically bound inthe polymer matrix, without a separate capsule wall.Diffusion-controlled release also takes place when polymeric carriermaterials are hydrophobic and less available to the metabolism of higherplants than to that of microorganisms. For example, this applies topolyhydroxy butyrate/polyhydroxy valerate copolymers.

Microcapsules whose matrices remain intact in the use region serve asactive substance depot preparation, and they are therefore used ininjections for long-term treatments, e.g., in treating the death ofelms.

It is essential for the present invention that microparticles having amaximum size of 100 μm be used. The particular advantage of thisdimensioning is the particle mobility in the plant that can be achievedthereby. In contrast to prior art particulate active substance carrierswhose particle diameters are in the range of 100-3000 μm, the size ofthe particles used in the injection process according to the presentinvention corresponds to the average size of plant cells (10-100 μm),Thus their transport in the tissue region which is particularlyimportant for substance distribution in the leaves can considerably beimproved because the microbeads are diffusible owing to their relativelysmall size with given stability. In addition there is the advantage ofgood mobility in the plant's paths of conduction; this also applies toplants having small-luminal sieve tubes.

Particles based on water-soluble polysaccharides (e.g., starch,alginates, carragheenan and pectins) represent a preferred embodiment ofthe particulate active substance carriers used in the process accordingto the present invention. Since their polymer matrix can quite rapidlybe converted into osmotically effective substances (e.g.,oligosaccharides) within the plant organism, they are preferablytransported in the phloem. This is particularly advantageous whengrowing parts of the plant (meristems) are to be provided with activesubstances.

Among the active substances which can be injected by means of theprocess according to the present invention in particulate form, thoseare to be mentioned which are capable of influencing processes in theanimal or plant organism. These primarily include systemically activeplant protection agents, for example, insecticides, acaricides,fungicides, and bactericides.

Systemic insecticides include, for example, butocarboxim, dimethoate,fenoxycarb, methamyl, oxamyl, oxydemeton-methyl, pirimicarb, orpropoxur.

Systemic acaricides include, for example, clofentizine, fenbutatinoxide, and hexythiazox.

Systemic fungicides include, for example, benomyl, bromuconazole,bitertanole, etaconazole, flusilazol, furalaxyl, fosetyl-Al, imazalil,metalaxyl, penconazole, propiconazole, thiabendazol, triadimefon,triadimenol, or triforine.

Flumequine, for example, is to be mentioned among the systemicbactericides. Systemic growth regulators include, for example, ethephonand β-indolylacetic acid (IAA).

Another advantage achievable by means of the present invention is thefact that the desired injection media may be present both in flowableand solid form. The problem of needle occlusion occurring inconventional injection systems is avoided because here nozzle injectionof small-sized microparticles is concerned.

Particularly preferable is a process wherein the composition accordingto the present invention, which is to be injected, is formulated inliquid vehicles. Suitable liquid vehicles include water, NPKmineralfertilizer solution, and vegetable oils. Water is to be emphasized asparticularly preferable.

Adjuvants may be added as required. These may include dispersants, suchas polysorbat 80, or thickeners, such as carboxymethylcellulose.Depending on the production method in the process according to thepresent invention, other adjuvants known to the skilled artisan may alsobe included.

The present invention will be illustrated by means of the followingExample:

EXAMPLE 1

8.8 g poly-D,L-lactide-co-glycolide (molar ratio 50:50) is dissolved in240 ml dichloromethane and placed in a reaction vessel equipped with astirrer. 0.36 g of the active substance Al-fosetyl is suspended at astirring rate of 500 rpm. Subsequently, 54 g sesame oil is progressivelyadded under continued stirring. After complete addition of sesame oil,the mixture comprising the raw microcapsules is continuously dispersedin a thin jet under constant stirring (at 1000 rpm) in 4l of acaprylic-capric acid triglyceride (Miglyol® 812, viscosity 27 to 33mPa.s) at 20° C. Hardening of the microcapsules takes place within aperiod of 60 min. The microcapsules thus obtained are filtered off,washed twice with isopropanol, and dried. The particles comprise2.8%-wt. of the active substance. The average particle diameter amountsto 25.5 μm. Immediately prior to use, 270 mg microcapsules is suspendedat 37° C. in 120 ml water. The suspension thus obtained is filled into apressure-actuated injection device without needle (type Demo-Jet) andinjected at a pressure of 8.1 bar into the plant tissue at the basis ofa partially lignified biennal sprout (Rubus idaeus).

What is claimed is:
 1. A process for the administration of one or moreactive substances to plants, comprising:injecting into a plant or plantsa flowable solid, semi-solid or liquid medium exhibiting a controlledrelease of at least one active substance by means of injection usingneedle-free, pressure-actuated devices, wherein said medium comprisesactive substance-containing microparticles of a maximum size of 100 μmincluding the following components:(a) 0.5-70%-wt. of at least oneactive substance, (b) 10-70%-wt. of at least one biodegradable polymer,(c) up to 20%-wt. of formulation adjuvants.
 2. The process according toclaim 1, wherein said microparticles are present as a dispersion in anaqueous phase.
 3. The process according to any of claims 1 or 2, whereinsaid biologically degradable polymers are selected from the groupconsisting of polylactic acid, polyglycolic acid, polylactides as wellas their copolymers, cellulose and its derivatives, aliphaticpolyesters, and polysaccharides.
 4. The process according to claim 3,wherein said polysaccharides comprise water-soluble polysaccharrides,selected from the group consisting of starch, alginic acids and theirsalts, carragheenans, and pectins.